Methanol synthesis from coal

The use of an MHTGR was studied for methanol synthesis from coal without CO2 production. Besides coal and steam, the process requires a supplemental hydrocarbon feed or ideally hydrogen, also methane could be used, plus a non-combustion source of high-temperature heat which is ideally an HTGR. Based on coal with 60 % carbon content and a conversion rate of 80 %, a balance of the process was predicted such that with an input of 162 t/h of coal and 69.4 t/h of methane and an electric power of 300 MW yields 347 tb of methanol [64]. 

Countries with large domestic coal reserves, such as China and South Africa, rely primarily on coal gasification to produce synthesis gas. This synthesis gas is hydrogen deficient (M < 2) and must undergo a further water-gas shift (WGS) step to yield a C02-rich mixture [2]. Methanol synthesis from C02 and C02-rich mixtures provides special catalyst and reactor design challenges, which will be further discussed in more detail. 

Sulfur poisoning is a key problem in hydrocarbon synthesis from coal-derived synthesis gas. The most important hydrocarbon synthesis reactions include methanation, Fischer-Tropsch synthesis, and methanol synthesis, which occur typically on nickel, iron, or cobalt, and ZnO-Cu catalysts, respectively. Madon and Shaw (2) reviewed much of the early work dealing with effects of sulfur in Fischer-Tropsch synthesis. Only the most important conclusions of their review will be summarized here. 

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Liquid Fuels via Methanol Synthesis and Conversion. Methanol is produced catalyticaHy from synthesis gas. By-products such as ethers, formates, and higher hydrocarbons are formed in side reactions and are found in the cmde methanol product. Whereas for many years methanol was produced from coal, after World War II low cost natural gas and light petroleum fractions replaced coal as the feedstock. 

There are some chemicals that can be made economically from coal or coal-derived substances. Methanol and CO are used to make acetic anhydride and acetic acid. Methanol itself can be made from synthesis gas over a copper-2inc catalyst (see Feedstocks, coal chemicals). 

Hydrocarbons from Synthesis Gas and Methanol. Two very important catalytic processes in which hydrocarbons are formed from synthesis gas are the Sasol Eischer-Tropsch process, in which carbon monoxide and hydrogen obtained from coal gasification are converted to gasoline and other products over an iron catalyst, and the Mobil MTG process, which converts methanol to gasoline range hydrocarbons using ZSM-5-type 2eohte catalysts. 

Methanol is usually prepared industrially from synthesis gas, which is obtained from coal (Section 14.3) ... 

Depending on the nature of the raw material (coal, natural gas, naphtha), both the reaction conditions of gasification, and the employment of reforming (shift conversion) will determine the composition of the syngas. For instance, synthesis gas produced from coal normally has a H2 C0 ratio of unity and therefore the ratio has to be adjusted to 2.0 prior to the use of the gas for methanol synthesis. Accordingly, syngas derived from CH4 bears a cost advantage for the needed ratio of 2.0. 

Methanol was first produced commercially in 1830 by the pyrolysis of wood to produce wood alcohol. Almost a century later, a process was developed in Germany by BASF to produce synthetic methanol from coal synthesis gas. The first synthetic methanol plant was introduced by BASF in 1923 and in the United States by DuPont in 1927. In the late 1940s, natural gas replaced coal synthesis gas as the primary feedstock for methanol production. In 1966, ICI announced the development of a copper-based catalyst for use in the low-pressure synthesis of methanol. 

Twenty-five years ago the only oxygenated aliphatics produced in important quantities were ethyl and n-butyl alcohols and acetone made by the fermentation of molasses and grain, glycerol made from fats and oils, and methanol and acetic acid made by the pyrolysis of wood. In 1927 the production of acetic acid (from acetylene) and methanol (from synthesis gas) was begun, both made fundamentally from coal. All these oxygenated products are still made from the old raw materials by the same or similar processes, but the amount so made has changed very little in the past quarter century. Nearly all the tremendous growth in the production of this class of compounds has come from petroleum hydrocarbons. 

The current two-step industrial route for the synthesis of methanol, from coal or methane to synthesis gas and then from synthesis gas to methanol, has certain drawbacks. The economic viability of the whole process depends on the first step, which is highly endothermic. Thus a substantial amount of the carbon source is burned to provide the heat for the reaction. It would be highly desirable, therefore, to replace this technology with a technically simpler, single-step process. This could be the direct partial oxidation of methane to methanol, allowing an excellent way to utilize the vast natural-gas resources. Although various catalysts, some with reasonable selectivity, have been found to catalyze this reaction (see Sections 9.1.1 and 9.6.1), the very low methane conversion does not make this process economically feasible at present. 

Figure 17.24. Types of reactors for synthetic fuels [Meyers (Ed.), Handbook of Synfuels Technology, McGraw-Hill, New York, 1984], (a) ICI methanol reactor, showing internal distributors. C, D and E are cold shot nozzles, F = catalyst dropout, L = thermocouple, and O = catalyst input, (b) ICI methanol reactor with internal heat exchange and cold shots, (c) Fixed bed reactor for gasoline from coal synthesis gas dimensions 10 x 42 ft, 2000 2-in. dia tubes packed with promoted iron catalyst, production rate 5 tons/day per reactor, (d) Synthol fluidized bed continuous reactor system for gasoline from coal synthesis gas.

In the future, there is no doubt that alcohols will play a major role not only as fuel components (70,71) but also as feed stocks for the syntheses of more complicated organic compounds (72). A great amount of research effort is presently directed to the economic conversion of CO and to methanol (73), and on homologation of methanol to higher alcohols (74). Conversion of synthesis gas from coal to acetic anhydride (75) through the intermediacy of methyl acetate (from methanol) will soon be a commercial reality. 

Of the indirect liquefaction procedures, methanol synthesis is the most straightforward and well developed [Eq. (6)]. Most methanol plants use natural gas (methane) as the feedstock and obtain the synthesis gas by the steam reforming of methane in a reaction that is the reverse of the methanation reaction in Eq. (5). However, the synthesis gas can also be obtained by coal gasification, and this has been and is practiced. In one modern low-pressure procedure developed by Imperial Chemical Industries (ICI), the synthesis gas is compressed to a pressure of from 5 to 10 MPa and, after heating, fed to the top of a fixed bed reactor containing a copper/zinc catalyst. The reactor temperature is maintained at 250 to 270°C by injecting... 

This is one of the reasons I brought up the liquids from synthesis gas as an ideal combination for the utility which would provide the methanol that is needed for the tip of the peak, and also possibly an ideal hydrocarbon turbine fuel which you will never get without a great deal of processing from coal through hydrogenation. 

Methanol production today is not a sustainable process but is part of a petrochemical route for conversion of fossil carbon into chemicals and fuels (see Section 5.3.3). It has to be emphasized that a one-to-one upscaling of existing industrial methanol synthesis capacities for fuel production is not useful. This is mainly because the current industrial process has not been developed and optimized under the boundary conditions of conversion of anthropogenic C02, but rather for synthesis gas feeds derived from fossil sources such as natural gas or coal. The switch to an efficient large-scale methanol synthesis with a neutral C02 footprint is still a major scientific and engineering challenge, and further research and catalyst and process optimization is urgently needed to realize the idea of a sustainable methanol economy. ... 

The purge gas from the methanol synthesis unit contains mainly methane. Depending upon the size of the plant, this stream may be reformed to supplement the synthesis gas produced from coal gasification. 

In the new Eastman process, synthesis gas (carbon monoxide and hydrogen) is made from coal. Then, from the generated synthesis gas, methanol was prepared. (Prior to this time, methanol had been made from methane, i.e., natural gas.)... 

The Frost group [80, 81] has been particularly active in devising microbial and chemical-microbial procedures for the benzene-free synthesis of phenolic compounds from glucose via the hydroaromatic compounds DHS, QA and SA. As has been noted previously, such products can be synthesized more cheaply from coal via the methanol route, if oil should become too expensive [82]. 

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